Originally, expansible full panel envelopes with gusseted side and bottom panels required a separate and independent procedure to tuck in the bottom gusset during fabrication. See for example, U.S. Pat. No. 2,899,874 wherein an additional step was necessary to crush in the bottom gusset after completion of the operations.
In prior U.S. Pat. Nos. 3,414,185, 3,552,640, and, 3,860,164, there are illustrated respectively a center seam, a side seam and a full panel expansible gusset envelope in which all side and bottom gussets are inwardly folded upon the completion of automatic machinery operations. However, each of these envelopes, as a result of their blank design and the operational steps of fabrication, were somewhat deficient in that the junctures at the corners were not entirely closed at the completion of assembly. As a consequence, small articles, such as pencils, pens, clips and the like, had a tendency to fall through the partially sealed openings at the gusset corners produced by these envelope constructions.
In prior U.S. Pat. No. 4,016,808, there is shown a method and apparatus for making an expansible gusset envelope from a blank in which the corner gusset tabs had to be crimped or crushed inwardly during a phase of the operation in order to form a saddle preparatory to tucking therein the outer margins of the bottom gusset wall for sealing. While this design produced an expansible envelope having all gussets inwardly collapsed at the close of operations and wherein the corners were fully closed and sealed, the crimping step performed by high speed machinery had a tendency to throw a fair percentage of the moving blanks out of line. This in turn produced an unwanted number of rejects by virtue of unintentional creases and glue applications out of true registration.
It is therefore an object of this invention to provide an envelope blank and a method an apparatus for forming said blank into an expansible envelope having fully closed corners and with all gussets interiorly collapsed at the completion of operations.
Another object of this invention is to provide a method and apparatus for forming an expansible gusset envelope from a single blank by way of operations that produce very low shrinkage rates.
Other objects of this invention are to provide an improved method of the character described that is easily and economically produced, sturdy in construction, and highly efficient and effective in operation.